You might have a birding life list, but do you keep a birding bucket list? Well you should, and we want to help you build one. In this new series, we'll be highlighting avian adventures every birder should try to check off, from visiting extraordinary gatherings across the globe to finding a rare bird in a remote location. And at the end of each article, we'll also include a few handy tips on what you should know before heading out.

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What: Giant flocks of feasting Short-tailed Shearwaters

Where: The chilly, open waters of Unimak Pass in Alaska’s eastern Aleutian Islands

When: July and early August

Witnessing the Short-tailed Shearwaters of Unimak Pass can take some work, but it’s worth the effort to watch a floating flock that can stretch as far as the eye can see. It's been estimated that as many as 16 million birds visit the pass every year, and they can linger in crowds of tens of thousands—sometimes possibly even more than a million—at once. “It’s really hard to get estimates,” says Suzi Golodoff, an Alaskan wildlife expert. “People try to do counts, but it’s pretty tough when you have those huge numbers.”

Every summer, Short-tailed Shearwaters fly more than 6,500 miles north from their breeding grounds in New Zealand and Australia to stuff their beaks in the waters between Aleutian Islands and into the Bering Sea. Unimak Pass is a wide eastern gap where the mixing waters result in a food-rich ecosystem. And each year as sea ice retreats, sunlight reaches fast-growing photosynthetic plankton, which fortifies the base of the food chain. All together, this makes for huge numbers of microscopic critters such as krill and small fish such as sandlance for Short-tailed Shearwaters to gobble down during their visit.

Jeff Williams has seen some of the largest of these gatherings thanks to his 27-year career at the Alaska Maritime National Wildlife Refuge, where he supervises and coordinates a range of research. The refuge’s main focus is studying birds that breed in the area, so Williams and his colleagues only try to count the shearwaters when they arrive. He estimates the largest aggregation he’s seen stretched for 30 miles. “You can’t guarantee that you’ll see that,” Williams says. “Sometimes you just happen to be in the right place at the right time.”

Being in the right place at the right time matters for the birds, too. Occasionally, they'll arrive to find they missed the feast due to an abnormality somewhere along the food chain. “They can be late, there can be this timing mismatch,” Williams says. “They need prey in the right places at the right time.” As the climate changes, it could increase this risk by nudging plankton blooms earlier in the year.

Another concern for the birds is the chance of an oil spill, since Unimak Pass is also a popular shipping lane during the summer months, according to Kathy Kuletz, a seabird biologist at U.S. Fish and Wildlife’s Alaska office. The pass is particularly busy during the summer, when crews can avoid Alaska’s harsh and dangerous winter weather. Even in July, it’s hardly an easy trip for ships, but that doesn’t stop the shearwaters. “It’s the most rugged of weathers, and it’s howling out,” Williams says. “They’re just in their element. They’re beautiful birds, they’re so graceful.”

Of course, there’s no guarantee that visiting Unimak Pass will earn you a glimpse of a shearwater feeding frenzy. The birds don’t stick around the pass long, following their food further north until the brisk autumn winds begin to sweep over the islands and send the birds back to Australia and New Zealand for breeding. “We’re just the dinner plate up here in Alaska,” Williams says.

Know before you go: To see the sprawling rafts of shearwaters, you’ll need access to a boat. Golodoff recommends taking the ferry Tustumena, which is scheduled to run every other week between Homer and Dutch Harbor, the port on Unalaska Island just west of Unimak Pass. Some visitors fly one way and take the ferry the other, she says. And be aware that even in the summer, weather in Alaska can still be rough—sometimes enough to interfere with the ferries and other boats. So it’s smart to add extra time to your trip just in case. Besides, there’s plenty of other wildlife to see if the shearwaters don’t cooperate. Keep an eye out for seabirds such as Laysan Albatross and, particularly, the Whiskered Auklet, a specialty of the Aleutians.

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